Railroads use a vast number of track safety standards to protect railway workers, the environment, private property, and prevent derailments. These safety standards generally require track geometry measurements to be within a certain range for a certain class of track. Track speed limits increase class number, requiring specifications that are more stringent be met. Basic geometry parameters include gage, the distance between the rails, and cross-level, the difference in height of the rails. Curvature is another important track geometry parameter. Curvature is the difference in heading of two locations 100 feet apart expressed in degrees. Two additional parameters are alignment and profile.
In the field of railway inspection, track alignment and profile are measured as the mid-chord offset (MCO) of a specified chord length at a known contact point on the rail to be measured. The endpoints of the chord lie on the rail and a measurement is taken at the center of the chord. The alignment and profile MCO values are taken in the lateral (horizontal) and vertical planes respectively. Common chord lengths are thirty one feet, sixty two feet and one hundred twenty four feet with the longer chord lengths being used on higher classes of track.
Track geometry cars have used an inertial method to calculate profile and alignment. Vertical and lateral acceleration data, referenced to each rail individually, can be used to produce localized space curves. From the space curve data, MCO values of any desired chord length can be calculated. Unfortunately, inertial means are not an option when statically measuring MCO values in the field. A long accepted practice has been to stretch a string of the desired chord length between two points on the rail and measure the distance from the center of the string to the rail in both the vertical and lateral planes. Although not extremely accurate, this method gives acceptable results when using a 31-foot chord. Recent increases in track speed have led to safety standards that require the measurement of 62 and 124-foot chords. The use of string to measure these chord lengths provides rather imprecise data. Sag and sway of the string both greatly influence the measurement of profile and alignment.
A primary object of the present invention is to provide a novel and improved method and apparatus for track geometry measurement using an optical technique to produce accurate measurement of track geometry.
Another object of the present invention is to provide a novel and improved method and apparatus for track geometry measurement which provides alignment and profile measurements based upon the mid-chord offset (MCO) of a specified chord length at a known contact point on a railroad track to be measured.
Yet another object of the present invention is to provide a novel and improved method and apparatus for railroad track geometry measurement using optical techniques to obtain MCO data for 31 foot chords and to employ this data to extrapolate MCO values for longer chords.
A further object of the present invention is to provide a novel and improved compact, lightweight unit for track geometry measurement using optical techniques to measure railroad track alignment and profile.
A still further object of the present invention is to provide a novel and improved apparatus for track geometry measurement using back to back CCD cameras and targets a known distance ahead of and behind the cameras to provide an MCO offset measurement for both profile and alignment. Sensors are also provided to measure gage and cross-level of railroad tracks.
These and other objects of the present invention are achieved by providing a rolling trolley engaging the parallel rails of a railroad track which bears two CCD cameras placed back to back relative to a central gage bar for the trolley which extends across the rails of the track. The configuration of the cameras defines a coordinate system with its origin at the center of the cameras and the X-axis passing through the center of the camera lenses. Two target bearing shoes ride on a rail 15.5 feet ahead of and behind the origin on the trolley and are held in place by rods extending from the gage bar. MCO is calculated by optically measuring the position of two targets on the shoes which are at a known position relative to the ⅝xe2x80x3 contact point on a rail. By knowing the relative displacements of the targets, it is possible to calculate both the horizontal and vertical MCO from which profile and alignment of a measured rail can be calculated.